We propose a study of isolated heart muscle using a system of load control with a high speed servomotor and computer-controlled feedback techniques to simulate the loading sequence characteristic of the intact ventricle. Despite increasing evidence that loading conditions significantly effect the parameters of contraction, present mechanical studies of isolated mammalian myocardium are sequentially incorrect so that grossly abnormal loading conditions are seen by the muscle preparation. As a result of preliminary studies using electronic hardware, it has been concluded that a computer based system would provide a degree of flexibility not possible in the previous system and necessary for the dynamic assessment of heart muscle function. The basic idea of the proposed project is to control physiologically and in proper sequence either muscle length or load while observing the variable or uncontrolled parameter. This system will provide basic information concerning the function of heart muscle under normal and pathologic conditions. It is also anticipated that this device will provide a somewhat different approach to currently active topics such as active state, muscle models and contractile state assessment.